U.s. pat. No. 407,313 PA0 U.s. pat. No. 484,848 PA0 U.s. pat. No. 522,578 PA0 U.s. pat. No. 539,186 PA0 U.s. pat. No. 689,760 PA0 U.s. pat. No. 2,449,092 PA0 U.s. pat. No. 2,800,879 PA0 U.s. pat. No. 3,852,843